David Mattingly's cover for the T20 book is great, as are most of the GT covers (especially the Jesse DeGraff computer renderings). I'd like to see T^5 have cover art on the same level as those (assuming it actually has cover art and we don't see the return of the LBBs, that is). I'm also a big fan of A.C. Farley's MT-era covers (
Rebellion Sourcebook,
World Builder's Handbook). Christopher Sly's artwork has a more of a 'gothic' flavor than I traditionally associate with Traveller so I wouldn't include him -- it's IMO
very important to avoid the "T4 syndrome" of artwork that doesn't fit the established look and feel of the milieu. The feel of Traveller is not Space-Gothic or Cyberpunk or Anime or Neo-psychedelic, and its artwork shouldn't be either, no matter how kewl it looks or how good a deal the publisher got on it.
For interiors, I think a lot of the existing Traveller line art from the likes of Dietrick, Danforth, Barr, Keith, Gibson, Caswell, Reynolds, etc. is very good and I'd happily see it recycled. The comic book/cartoon style of the interior art in TNE, T20, and (to a slightly lesser extent) GT I don't like nearly as well. Interior art should be used relatively sparingly, and the pictures should be kept small -- nothing screams "filler" to me so much as full-page non-functional illustrations (i.e. most of the artwork in T4, too much of it in T20). The quantity and quality of interior illos in
The Traveller Book, the 3 core MT books, and the late-period DGP stuff (
The Flaming Eye, S&A) are IMO pretty much ideal (though I'd like more realistic/detailed (and preferably Bryan Gibson-drawn

) illos of weapons and gear than we got in those). I'd avoid watercolors/paintings and computer renderings as interior illos unless the books have color interiors (which I don't think they should -- keeping production costs low will surely be a priority for T^5).